Natural gas production sites and crude oil production sites producing associated natural gas may be situated at great distances from markets where the natural gas or crude oil and associated gas are ultimately consumed. Therefore, the natural gas or crude oil and associated natural gas must be treated and processed prior to being transported from the production site to the market where it can be offloaded.
One solution is to use a pipeline network. However, this presupposes that an existing pipeline network is available in the relative vicinity of the production and consumption site. If not, the time and capital required to extend a pipeline network to a remote production site can be cost prohibitive. Further, environmental and safety risks associated with the pipeline may deter the extension of the pipeline and its operation.
Another solution is to store the natural gas as compressed natural gas (CNG). Compressed natural gas is made by first treating raw natural gas to remove natural gas liquids (NGLs) and impurities such as acid gases, primarily carbon dioxide and hydrogen sulphide, and then compressing it in containers at high pressures (2900-3600 psi) into the dense phase for the specific treated raw natural gas composition. CNG is conventionally compressed to less than 1% of the volume it occupies at standard atmospheric pressure.
Another solution is to cryogenically convert raw natural gas to liquefied natural gas (LNG) for storage and transportation by truck, train or ship. Conventionally, the production of LNG involves pre-treating the raw natural gas to remove impurities such as nitrogen, water vapour, carbon dioxide, hydrogen sulphide, n-butane, neo-pentane, n-pentane, n-hexane, benzene, and cyclohexane, which would otherwise freeze, and mercury, which would amalgamate with the metal processing equipment. The treated natural gas is then condensed from a gaseous to an energy-dense liquid state by cooling the gas to approximately −160° C. at near atmospheric pressure. Although the energy density of LNG is greater than that of CNG, the production of LNG production is energy and capital-intensive and requires expensive specially-designed LNG carriers to maintain cryogenic conditions during transport, and expensive specially designed re-gasification facilities at the offloading point.
Crude oil is often produced with dissolved raw natural gas. Conventionally, the associated natural gas is separated from the crude oil at the production site or central processing facility and processed separately. The associated gas may be flared, consumed as fuel, re-injected into the reservoir, processed further into sales gas by removing impurities (such as H2S and CO2) and NGLs, depending on available markets, economics, environmental considerations, and other factors. The crude oil may be treated to remove free-water, salts, and other impurities as required to meet specifications (such as BS&W, and vapour pressure) prior to transport by pipeline, truck, rail, or ship to markets for further processing into refined products.
In both cases of natural gas production and crude oil production, there is a need to reduce equipment needs and capital costs at production sites for loading storage and transport vessels.
Accordingly, there remains a need in the art for a method of storing, transporting, and offloading to market raw natural gas or crude oil and associated natural gas that is energy efficient, economical and practical to implement.